Optical Article Coated with an Antireflection Coating Comprising a Sublayer Partially Formed under Ion Assistance and Manufacturing Process

ABSTRACT

The invention relates to an optical article provided with antireflection properties, comprising a substrate having at least one main surface coated with an antireflection coating comprising, starting from the substrate:
         a sub-layer comprising two adjacent layers formed from the same material, the sum of the thicknesses of the two adjacent layers being greater than or equal to 75 nm; and   a multilayered antireflection stack comprising at least one high refractive index layer and at least one low refractive index layer,   the deposition of the first of said two adjacent layers of the sub-layer having been carried out without ion assistance and the deposition of the second of said two adjacent layers of the sub-layer having been carried out under ion assistance.       

     The invention also relates to a process for manufacturing such an optical article.

The invention relates to an optical article comprising a substratecoated with an antireflection coating comprising a sub-layer, having inparticular an improved abrasion resistance, as well as a process formanufacturing such an optical article.

In the ophthalmic optics field, it is usual to coat an ophthalmic lenswith various coatings so as to impart various mechanical and/or opticalproperties to this lens. Thus, classically, coatings such asimpact-resistant, anti-abrasion and/or antireflection coatings aresuccessively formed onto an ophthalmic lens.

An antireflection coating is defined as being a coating, deposited ontothe surface of an optical article, which improves the antireflectionproperties of the final optical article. It enables to reduce the lightreflection at the article-air interface within a substantially broadrange of the visible spectrum.

Anti-reflection coatings are well known and classically comprise amono-layer or multi-layer stack of dielectric materials such as SiO,SiO₂, Al₂O₃, MgF₂, LiF, Si₃N₄, TiO₂, ZrO₂, Nb₂O₅, Y₂O₃, HfO₂, Sc₂O₃,Ta₂O₅, Pr₂O₃, or combinations thereof.

As is also well known, antireflection coatings are preferablymultilayered coatings comprising alternatively high refractive indexlayers and low refractive index layers.

It is known to interleave a relatively thick sub-layer between thesubstrate and the high refractive index and low refractive index layersof the antireflection coating so as to improve the abrasion resistanceand/or scratch resistance of said coating. This sub-layer may compriseone or more layer(s).

The deposition of the layers forming the sub-layer and the multilayeredantireflection stack is traditionally made by vapor phase deposition,optionally under ion beam assistance. The ion assisted deposition methodor IAD is notably described in the US patent application 2006/017011 andin the U.S. Pat. No. 5,268,781. It does not require any heating of thesubstrates, which is interesting for coating heat-sensitive substratessuch as glass or plastic substrates.

The evaporation under ion assistance consists in depositing onto asubstrate a film of material by vacuum evaporation by simultaneouslybombarding the surface of the substrate with an ion beam delivered by anion gun. The ion bombardment leads to an atomic rearrangement in thecoating being formed, which increases its density. The IAD not onlyallows an improvement of the deposited layer adhesion, but also anincrease in their refractive index.

The patent application WO 2005/059603, in the name of the applicant,describes an ophthalmic lens substrate coated with a multilayeredcolored antireflection coating, deposited without ion assistance, andwith an anti-fouling coating. The antireflection coating is composed ofa 100-110 nm-thick silica sub-layer, and of visible-absorbing,substoichiometric titanium dioxide TiO_(x) (x<2)-based, alternating highrefractive index layers and low refractive index layers (LI) based onSiO₂ doped with 1-5% by weight of Al₂O₃, relative to the total weight ofSiO₂+Al₂O₃.

Prior to depositing the antireflection coating, the surface of thesubstrate is submitted to a treatment to improve the adhesion of thesub-layer. This surface preparation, called IPC (Ion Pre-cleaning) doesconsist in an ion bombardment pre-cleaning of the substrate throughargon ions using an ion gun.

The optical article manufactured according to the teaching of the patentapplication WO 2005/059603 has good abrasion resistance properties,which may nevertheless be further improved.

The Japanese patent H05-034502 describes the preparation of opticalarticles comprising an antireflection coating composed of a 0.125λ to0.8λ-thick laminated sub-layer, with λ=500 nm and of an antireflectionstack comprising a high refractive index layer interleaved between twolow refractive index layers.

The laminated sub-layer comprises the following three layers, that allhave been deposited without ion assistance: a SiO₂ layer with a lowthickness (0.05λ-0.15λ) and a refractive index n=1.45-1.47, a Ta₂O₅layer with a very low thickness (0.01λ-0.10λ) and a refractive indexn=2-2.1, and a SiO₂/Al₂O₃ layer with a high thickness (0.75λ-1.50λ) anda refractive index n=1.48-1.52, these three layers being deposited ontothe substrate in the order they have been mentioned.

Using this three-layered sub-layer instead of a single SiO₂/Al₂O₃ layermakes it possible to improve the heat resistance properties of theoptical article. This patent does not relate to any abrasion resistanceimprovement.

The European patents EP 1184685 and EP 1184686 (Hoya Corporation)describe an optical element comprising a plastic substrate coated with aNb (niobium metal) or SiO₂ sub-layer and an antireflection stack. Thesub-layer (only if composed of niobium), and some layers within theantireflection stack may be deposited by evaporation under argon ionassistance. The thus prepared article has a good thermal and scratchresistance, knowing that the abrasion resistance thereof has not beenevaluated.

It is thus an objective of the present invention to provide atransparent optical article, in particular an ophthalmic lens,comprising a mineral or an organic glass substrate and an antireflectioncoating including a sub-layer, which does advantageously possess bothabrasion resistance and adhesion properties improved as compared to theoptical articles of the prior art.

The prepared optical articles should retain outstanding transparencyproperties, have a good resistance to a hot water-dip treatment followedwith a superficial mechanical stress, and be free of any opticaldefects.

A further objective of the invention is a method for manufacturingoptical articles such as previously mentioned, which could be easilyintegrated into the classical optical article manufacturing chain andwould preferably avoid heating the substrate.

The previously mentioned inventors have found that modifying the processfor making the antireflection coating sub-layer would enable to aim atall the previously mentioned objectives.

The hereabove mentioned objectives are thus aimed at according to theinvention through an optical article with antireflection properties,comprising a substrate having at least one main surface coated with anantireflection coating comprising, starting from the substrate:

-   -   a sub-layer comprising two adjacent layers which are preferably        formed from the same material, the sum of the thicknesses of        these two adjacent layers being greater than or equal to 75 nm;        and    -   a multilayered antireflection stack comprising at least one high        refractive index layer and at least one low refractive index        layer,

the deposition of the first of said sub-layer two adjacent layers havingbeen carried out without ion assistance and the deposition of the secondof said sub-layer two adjacent layers having been carried out under ionassistance.

The invention further relates to a manufacturing process of such anoptical article provided with antireflection properties, comprising atleast the following steps of:

providing an optical article comprising a substrate having at least onemain surface;

depositing onto a main surface of the substrate a sub-layer having anexposed surface, where said sub-layer comprises two adjacent layerswhich are preferably formed from the same material, the deposition ofthe first of these two adjacent layers being carried out without ionassistance, the deposition of the second of these two adjacent layersbeing carried out under ion assistance, and the sum of the thicknessesof the two adjacent layers being greater than or equal to 75 nm;

depositing onto said exposed surface of the sub-layer a multilayeredantireflection stack comprising at least one high refractive index layerand at least one low refractive index layer,

recovering an optical article comprising a substrate having one mainsurface coated with an antireflection coating comprising said sub-layerand said multilayered stack.

In the present application, when an optical article is provided with oneor more coating(s) on its surface, “depositing a layer or a coating ontothe article” is intended to mean that a layer or a coating is depositedonto the visible surface (exposed) of the article external coating, thatis to say its outermost coating relative to the substrate.

As used herein, a coating which lies “on” a substrate or which has beendeposited “onto” a substrate is defined as a coating which (i) ispositioned over the substrate, (ii) is not necessarily in contact withthe substrate, i.e. one or more intermediary coating(s) may be arrangedbetween the substrate and the coating of interest, and (iii) does notnecessarily cover the substrate in full.

When a “layer 1 is placed under a layer 2”, it means that the layer 2 isthe farthest from substrate as compared to the layer 1.

As used herein, an “antireflection multilayered stack” is intended tomean the multilayered stack of the antireflection coating which has beendeposited onto the antireflection coating sub-layer. In the followingdescription, it will be simply referred to as the “multilayered stack.”

The optical article prepared according to the invention comprises asubstrate, preferably transparent, in mineral or organic glass havingrear and front main faces, at least one of which being coated with ananti-reflection coating comprising a sub-layer coated with amultilayered stack, preferably both main faces thereof. The multilayeredstack does preferably directly contact the sub-layer.

As used herein, the rear face (generally the concave face) of thesubstrate is the face which, in use, is the closest to the wearer's eye.On the contrary, the front face (generally the convex face) of thesubstrate is the face which, in use, is the farthest from the wearer'seye.

Generally speaking, the sub-layer and the multilayered stack of theantireflection coating of the optical article of the invention may bedeposited onto any substrate, and preferably onto organic glasssubstrates, for example a thermoplastic or thermosetting plasticmaterial.

To be mentioned as thermoplastic materials to be suitably used assubstrates are (meth)acrylic (co)polymers, particularly methylpoly(methacrylate) (PMMA), thio(meth)acrylic (co)polymers,polyvinylbutyral (PVB), polycarbonates (PC), polyurethanes (PU),poly(thiourethanes), polyol allylcarbonate (co)polymers, thermoplasticcopolymers of ethylene/vinyl acetate, polyesters such as polyethyleneterephthalate (PET) or polybutylene terephthalate (PBT),polyepisulfides, polyepoxides, polycarbonate and polyester copolymers,cyclo-olefin copolymers such as copolymers of ethylene and norbornene orethylene and cyclopentadiene and combinations thereof.

By (co)polymer, it is meant a copolymer or a polymer. By (meth)acrylate,it is meant an acrylate or a methacrylate.

Preferred substrates of the invention include substrates obtained by thepolymerization of alkyl (meth)acrylates, in particular C₁-C₄ alkyl(meth)acrylates such as methyl (meth)acrylate and ethyl (meth)acrylate,polyethoxylated aromatic (meth)acrylates such as the polyethoxylatedbisphenolate di(meth)acrylates, allyl derivatives such as aliphatic oraromatic polyol allyl carbonates, linear or branched,thio(meth)acrylates, episulfides, and precursor mixtures of polythiolsand polyisocyanates (to give polythiourethanes).

As used herein, a polycarbonate (PC) means both homopolycarbonates andcopolycarbonates and block copolycarbonates. Polycarbonates arecommercially available, for example from the GENERAL ELECTRIC COMPANYunder the trade name LEXAN®, the TEIJIN company under the trade namePANLITE®, the BAYER company under the trade name BAYBLEND®, the MOBAYCHEMICHAL Corp. under the trade name MAKROLON® and the DOW CHEMICAL Co.under the trade name CALIBRE®.

Suitable examples of polyol allyl carbonate (co)polymers to be mentionedinclude (co)polymers of ethyleneglycol bis(allyl carbonate), ofdiethyleneglycol bis 2-methyl carbonate, of diethyleneglycol bis(allylcarbonate), of ethyleneglycol bis(2-chloro allyl carbonate), oftriethyleneglycol bis(allyl carbonate), of 1,3-propanediol bis(allylcarbonate), of propyleneglycol bis(2-ethyl allyl carbonate), of1,3-butenediol bis(allyl carbonate), of 1,4-butenediol bis(2-bromo allylcarbonate), of dipropyleneglycol bis(allyl carbonate), oftrimethyleneglycol bis(2-ethyl allyl carbonate), of pentamethyleneglycolbis(allyl carbonate), of isopropylene bisphenol A bis(allyl carbonate).

Particularly recommended substrates are the substrates obtained by(co)polymerization of diethyleneglycol bis allyl carbonate, marketed,for example, under the trade name CR-39® by the PPG Industries company(ESSILOR ORMA® lenses).

Other particularly recommended substrates further include substratesobtained by polymerization of thio(meth)acrylic monomers, such as thosedescribed in the French patent application FR 2 734 827.

The substrates may obviously be obtained by polymerizing mixtures of theabove monomers or they also may comprise combinations of these polymersand (co)polymers.

Preferred organic substrates are those having a thermal expansioncoefficient ranging from 50.10⁻⁶° C.⁻¹ to 180.10⁻⁶° C.⁻¹, preferablyfrom 100.10⁻⁶° C.⁻¹ to 180.10⁻⁶° C.⁻¹.

Prior to depositing the sub-layer onto the substrate optionally coatedfor example with an abrasion- and/or scratch-resistant layer, it isusual to submit the surface of said optionally coated substrate, to aphysical or chemical activation treatment, to improve the adhesion ofthe sub-layer. This pre-treatment is generally carried out under vacuum.It may be a bombardment with energetic species, for example an ion beammethod (“Ion Pre-Cleaning” or “IPC”) or an electron beam method, acorona treatment, an ion spallation treatment, an ultraviolet treatmentor a plasma treatment under vacuum, typically an oxygen or an argonplasma. It may also be an acid or a base surface treatment and/or asolvent surface treatment (using water or an organic solvent). Manytreatments may be combined. Thanks to these cleaning treatments, thecleanliness of the substrate surface is optimized.

By energetic species, it is meant species with an energy ranging from 1to 300 eV, preferably from 10 to 150 eV, and more preferably from 10 to150 eV and most preferably from 40 to 150 eV. Energetic species may bechemical species such as ions, radicals, or species such as photons orelectrons.

The preferred pre-treatment of the substrate surface is the ionbombardment treatment, performed by means of an ion gun, the ions beingparticles made of gas atoms from which one or more electron(s) is or areextracted. Argon (Ar⁺ ions) is preferably employed as ionized gas, butalso oxygen, or combinations thereof, under an accelerating voltagetypically ranging from 50 to 200 V, a current density typically rangingfrom 10 to 100 μA/cm² on the activated surface, and typically under aresidual pressure in the empty chamber which may vary from 8.10⁻⁵ mbarto 2.10⁻⁴ mbar.

According to the present invention, a sub-layer is used in combinationwith a multilayered stack comprising at least one high refractive indexlayer and at least one low refractive index layer.

As used herein, a “sub-layer” or “an adhesion layer” is intended to meana coating that has been deposited onto the substrate (bare or coated)prior to depositing the multilayered stack of the invention. Thesub-layer should be sufficiently thick to promote the abrasionresistance of the antireflection coating, but preferably not to thepoint there are to much overall stress which may lead to adherenceproblems.

Because it is relatively thick, the sub-layer does not typically takepart to the anti-reflecting optical function, particularly where it hasa refractive index close to the bare substrate, if the sub-layer isdeposited onto the bare substrate, or close to the coating if thesub-layer is deposited onto a coated substrate.

The sub-layer of the invention is a multilayered sub-layer (laminated),preferably a bilayer. In the latter case, it does not comprise anyfurther layers other than both adjacent layers preferably formed fromthe same material and the sum of physical thicknesses of which isgreater than or equal to 75 nm.

The sum of these thicknesses is preferably greater than or equal to 80nm, more preferably greater than or equal to 100 nm and even morepreferably greater than or equal to 150 nm. The sum of the thicknessesof these two adjacent layers is typically lower than 250 nm, morepreferably lower than 200 nm.

The antireflection coating sub-layer of the invention comprises twoadjacent layers preferably of a similar chemical nature but havingdifferent characteristics because of the two different depositionmethods used.

Thus, the second of these two adjacent layers to be deposited doesposses a higher density as compared to that of the first one, because itwas formed under ion assistance whereas the first of these two adjacentlayers to be deposited was not. In the following, the first of these twoadjacent layers to be deposited will be referred to as being thesub-layer “lower layer” whereas the second of these two adjacent layersto be deposited will be referred to as being the sub-layer “higherlayer”.

These two adjacent layers of the sub-layer are preferably formed fromthe same material, which means then, in the context of the presentapplication, that they were formed from the same material, for exampleby evaporation of the same compound (or the same combination ofcompounds).

The lower layer and the higher layer of the sub-layer are preferablySiO₂-based layers. They may comprise in addition to silica, one or moreother materials traditionally used for forming sub-layers, for exampleone or more materials selected from the dielectric materials hereaboveand hereafter described in the present specification. There arepreferably, SiO₂-based layers that are free of Al₂O₃, and mostpreferably they consist in SiO₂.

The lower layer and the higher layer of the sub-layer of the presentinvention preferably comprise at least 70% by weight of SiO₂, morepreferably at least 80% by weight and even more preferably at least 90%by weight of SiO₂. As already stated, they each comprise in an optimalembodiment 100% by weight of silica.

The thickness ratio of the sub-layer lower layer to the sub-layer higherlayer does preferably range from 9:1 to 1:9, more preferably from 4:6 to6:4. Depending on the embodiment illustrated in the experiment section,this ratio is 1:1. The thicknesses that are mentioned in the presentapplication are physical thicknesses, unless otherwise stated.

When formed from the same material, the lower layer and the higher layerof the sub-layer may be differentiated, in particular by means of atransmission electron microscopy, by an ion beam analysis (RBS) or,where possible, may be evidenced by diffusing a colored material, usingtheir different porosities.

The sub-layer of the invention comprises at least the two previouslymentioned adjacent layers. It may comprise additional layers, preferablyat most three additional layers, more preferably at most two otherlayers, interleaved between the optionally coated substrate and said twoadjacent layers, particularly if the optionally coated substrate has ahigh refractive index. These additional layers are preferably thinlayers, which function consists in restraining the reflections at thesubstrate-sub-layer interface (or at the abrasion- and/orscratch-resistant coating-sub-layer interface depending on thesituation).

Thus, when the substrate has a high refractive index (i.e. a refractiveindex greater than or equal to 1.55, preferably greater than or equal to1.57) and the sub-layer has been deposited directly onto the substrateor the substrate is coated with an abrasion- and/or scratch-resistantcoating with a high refractive index (that is to say greater than orequal to 1.55, preferably greater than or equal to 1.57), preferablybased on epoxysilanes, and the sub-layer has been deposited directlyonto this abrasion- and/or scratch-resistant coating, the sub-layercomprises preferably, in addition to the two adjacent layers preferablyformed from the same material and the sum of physical thicknesses ofwhich is greater than or equal to 75 nm, one layer with a highrefractive index and with a thickness lower than or equal to 80 nm, morepreferably lower than or equal to 50 nm and even more preferably lowerthan or equal to 30 nm. This layer with a high refractive index doesdirectly contact the high index substrate or the high index abrasion-and/or scratch-resistant coating. This embodiment may obviously be usedeven if the substrate (or the abrasion- and/or scratch-resistantcoating) has a refractive index lower than 1.55

As an alternative, the sub-layer comprises, in addition to the twoadjacent layers preferably formed from the same material and the sum ofphysical thicknesses of which is greater than or equal to 75 nm and tothe hereabove mentioned high refractive index layer, one layer composedof a low refractive index material (i.e. lower than or equal to 1.55,preferably lower than or equal to 1.52, more preferably lower than orequal to 1.50) based on SiO₂ and free of Al₂O₃ or not, with a thicknesslower than or equal to 80 nm, more preferably lower than or equal to 50nm and even more preferably lower than or equal to 30 nm, onto whichsaid high refractive index layer is deposited.

Typically, in this instance, the sub-layer comprises, that have beendeposited in this order starting from the substrate, a 25 nm-thick SiO₂layer, a 10 nm-thick ZrO₂ layer, said “lower layer” of the sub-layer andsaid “higher layer” of the sub-layer.

The various layers of the sub-layer are preferably deposited by vacuumevaporation.

The IAD operation the sub-layer higher layer does undergo may beperformed by means of an ion gun, where ions are particles composed ofgas atoms from which one or more electron(s) is or are extracted. Itdoes preferably consist in bombarding the surface to be treated withoxygen ions, having a current density typically ranging from 10 to 200μA/cm², preferably from 30 to 100 μA/cm² on the activated surface andtypically under a residual pressure in the empty chamber which may varyfrom 6.10⁻⁵ mbar to 2.10⁻⁴ mbar, preferably from 8.10⁻⁵ mbar to 2.10⁻⁴mbar. Other ionized gases may be used either combined with oxygen, ornot, as for example argon, nitrogen, in particular a mixture of O₂ andargon according to a volume ratio ranging from 2:1 to 1:2.

It is recommended not to deposit the sub-layer lower layer under ionassistance. Otherwise, it is as if a sub-layer comprising only one layerwith a thickness greater than or equal to 75 nm and a high density wasdeposited, which causes a decrease in the adhesion of someantireflection coating layers.

Without wishing to be bound to any particular theory, applicant believethat depositing a sub-layer with a thickness greater than or equal to 75nm under ion assistance gives a more dense sub-layer, which may resultin an excessive compression of the antireflection coating and thus maycause a decrease in the adhesion properties thereof. Conducting thedeposition of the sub-layer according to the process of the inventionenables to improve the abrasion resistance of the final article whilelimiting the increase in the compressive stress so as to avoid anyantireflection coating structural weakening.

The sub-layer of the invention has a total thickness greater than orequal to 75 nm, preferably greater than or equal to 80 nm, morepreferably greater than or equal to 100 nm and even more preferablygreater than or equal to 150 nm. Its thickness is typically lower than250 nm, more preferably lower than 200 nm.

The multilayered stack of the antireflection coating is preferablydeposited directly onto the exposed surface of the sub-layer, that is tosay directly onto the exposed surface of the sub-layer higher layer.

Optionally, the exposed surface of the sub-layer may be submitted, priorto depositing the first layer of the multilayered stack, to a physicalor a chemical activation treatment which may be selected from thepre-treatments the substrate may undergo prior to depositing thesub-layer and which have already be mentioned hereabove. The preferredpre-treatment is an ion bombardment. Traditionally conducted undervacuum, by using an ion gun-generated argon ion beam for instance, ittypically enables from the one hand to improve the abrasion resistanceproperties of the antireflection coating, and from the other hand toreinforce its adhesion properties, particularly the adhesion of themultilayered stack to the sub-layer.

Such physical or a chemical activation treatments may also be performedon the surface of one or more layer(s) of the multilayered stack,particularly on the surface of the next to last layer of this stack.

In the present application, a layer of the multilayered stack of theantireflection coating (AR) is said to be a high refractive index layer(HI) when its refractive index is greater than 1.55, preferably greaterthan or equal to 1.6, more preferably greater than or equal to 1.7, evenmore preferably greater than or equal to 1.8 and most preferably greaterthan or equal to 1.9. A layer of the multilayered stack of theantireflection coating is said to be a low refractive index layer (LI)when its refractive index is lower than or equal to 1.55, preferablylower than or equal to 1.52. more preferably lower than or equal to1.50.

Unless otherwise stated, the refractive indexes to which it is referredto in the present application are expressed at 25° C. for a wavelengthof 550 nm.

The HI layers are traditional high refractive index layers, well knownin the art. They typically comprise one or more mineral oxides such as,without limitation, zirconia (ZrO₂), titanium dioxide (TiO₂), tantalumpentoxide (Ta₂O₅), neodymium oxide (Nd₂O₅), praseodymium oxide (Pr₂O₃),praseodymium titanate (PrTiO₃), La₂O₃, Dy₂O₅, Nb₂O₅, Y₂O₃. Optionally,the high index layers may also contain silica or alumina, provided thattheir refractive index be greater than 1.55, preferably greater than orequal to 1.6, more preferably greater than or equal to 1.7 and even morepreferably greater than or equal to 1.9. Preferred materials includeTiO₂, PrTiO₃, ZrO₂ and combinations thereof.

According to a particular embodiment of the invention, at least one HIlayer of the multilayered stack is a TiO₂-based layer which highrefractive index is particularly interesting. It is preferably depositedunder ion assistance (IAD), which increases the compression of thislayer and thus its refractive index.

According to a further particular embodiment of the invention, at leastone HI layer of the multilayered stack is a PrTiO₃-based layer whichhigh thermal resistance is particularly interesting.

The LI layers are also well known and may comprise, without limitation,SiO₂, MgF₂, ZrF₄, alumina (Al₂O₃), AIF₃, chiolite (Na₃Al₃F₁₄), cryolite(Na₃[AlF₆]), and combinations thereof, preferably SiO₂ or SiO₂ dopedwith alumina, which contributes to increase the antireflection coatingthermal resistance. SiOF layers (SiO₂ doped with fluorine) may also beused. Of course, mixtures of these compounds with optionally one or moreother materials selected from the dielectric materials previouslydescribed in the present specification are such that the refractiveindex of the resulting layer is such as defined hereabove (1.55).

When a LI layer comprising a mixture of SiO₂ and Al₂O₃ is used, itpreferably comprises from 1 to 10%, more preferably from 1 to 8% andeven more preferably from 1 to 5% by weight of Al₂O₃ relative to thetotal weight of SiO₂+Al₂O₃ in this layer. An excessive amount of aluminamay be detrimental to the adhesion of the AR coating.

For example, SiO₂ doped with 4% or less Al₂O₃ by weight, or SiO₂ dopedwith 8% Al₂O₃ may be employed. Commercially available SiO₂/Al₂O₃combinations may be used, such as LIMA® marketed by Umicore Materials AG(refractive index n=1.48-1.50 at 550 nm), or L5® marketed by Merck KGaA(refractive index n=1.48 at 500 nm).

According to a preferred embodiment, at least one LI layer of themultilayered stack comprises a mixture of SiO₂ and Al₂O₃, preferablyconsists in a mixture of SiO₂ and Al₂O₃. According to another preferredembodiment, all the LI layers of the multilayered stack comprise amixture of SiO₂ and Al₂O₃, preferably consist in a mixture of SiO₂ andAl₂O₃. In the latter case, it is particularly preferred when the higherlayer and the lower layer of the sub-layer are SiO₂-based layers free ofAl₂O₃.

Typically, the HI layers have a physical thickness varying from 10 to120 nm, and the LI layers have a physical thickness varying from 10 to100 nm.

Preferably, the whole thickness of the antireflection coating is lowerthan 1 micrometer, more preferably lower than or equal to 800 nm andeven more preferably lower than or equal to 500 nm. The whole thicknessof the antireflection coating is typically higher than 100 nm,preferably higher than 150 nm.

Even preferably, the multilayered stack comprises at least two lowrefractive index layers (LI) and at least two high refractive indexlayers (HI). Preferably, the layer total number in the multilayeredstack is lower than or equal to 8, more preferably lower than or equalto 6.

LI and HI layers must not necessarily be alternated in the stack,although they also may according to an embodiment of the invention. TwoHI layers (or more) may be deposited onto one another; as well as two LIlayers (or more) may be deposited onto one another. It is thusinteresting as regards the abrasion resistance to stack onto one anotherfor example a ZrO₂ HI layer and a TiO₂ HI layer rather than using a TiO₂layer instead of these two adjacent HI layers.

The sub-layer is preferably adjacent to a high refractive index layer(HI) in the multilayered stack.

According to another preference, the outer layer of the multilayeredstack, that is to say the layer that is the most distant from thesubstrate, is a layer comprising a combination of silicon dioxide andaluminium oxide, in preferred amounts such as those previouslydescribed.

The various layers of the multilayered stack, the so called “opticallayers”, are preferably deposited by vacuum deposition according to oneof the following methods: i) by evaporation, optionally assisted by anion beam; ii) by spraying with an ion beam; iii) by cathode sputtering;iv) by plasma assisted chemical vapor deposition. These varioustechniques are described in “Thin Film Processes” and “Thin FilmProcesses II,” Vossen & Kern, Ed., Academic Press, 1978 and 1991,respectively. The particularly recommended technique is vacuumevaporation.

Preferably, the deposition of each of the antireflection coating layersis performed by vacuum evaporation. Such a process does advantageouslyavoid heating the substrate, which is particularly interesting fororganic glasses.

A treating step with energetic species such as previously defined mayalso be carried out, simultaneously with depositing one or more amongstthe various layers of the multilayered stack. In particular, workingunder ion assistance, preferably with oxygen ions, enables to pack saidlayers while they are being formed.

Optionally, the deposition of one or more layer(s) of the multilayeredstack and/or of the sub-layer is performed within a chamber under vacuumand with gas feeding during the deposition step. In concrete terms, agas such as, without limitation, argon, oxygen or combinations thereof,is introduced into the chamber for the deposition under vacuum while alayer is being deposited.

This modification to the process for depositing this layer generallyenables to limit the stress in the antireflection coating and toreinforce the adhesion of the layers thereof. When such depositionmethod is used, that is called deposition under gas pressure regulation,is used, it is preferred to work under an oxygen atmosphere (so called“passive oxygen”).

It is well known that optical articles have a tendency to get chargedwith static electricity, especially when they are cleaned under dryconditions by rubbing their surface with a cloth or with a piece of foamor polyester. As a consequence, they may attract and fix small particlesin the vicinity, such as dusts, as long as the charge remains on thearticle. It is well known in the art that an article can be renderedantistatic through incorporation in its surface of one electricallyconductive layer. Such method has been applied in the world patentapplication WO 01/55752 and in the patent EP 0834092. This layer helpsin quickly dissipating the charges.

By “antistatic”, it is meant the property of not retaining and/ordeveloping an appreciable electrostatic charge. An article is generallyconsidered to have acceptable antistatic properties when it does notattract or fix dust or small particles after one of the surfaces thereofhas been rubbed with an appropriate cloth.

Many methods exist for quantifying the antistatic properties of amaterial.

One of these methods consists in evaluating the static potential of thematerial. When the static potential of the material (measured when thearticle has not been charged) is 0 KV+/−0.1 KV (in absolute value), thematerial is said to be antistatic; on the contrary when its staticpotential is different from 0 KV+/−0.1 KV (in absolute value), thematerial is said to be static.

According to another method, the ability of a glass to evacuate a staticcharge created after rubbing with a cloth or any other electrostaticcharge generation process (charge applied by corona . . . ) can bequantified by measuring the time required for said charge to bedissipated. Thus, antistatic glasses have a discharge time in the orderof 100 milliseconds, preferably 200 ms or less, while static glasseshave a discharge time in the order of several tenth seconds.

The article of the invention can be rendered antistatic through theincorporation of at least one electrically conductive layer within themultilayered stack. The electrically conductive layer may be locatedanywhere in the antireflection coating, provided that it does not impairsignificantly the anti-reflection properties thereof. It may for examplebe deposited onto the sub-layer of the invention and thus form the firstlayer of the multilayered stack. It is preferably located between twodielectric layers of the multilayered stack and/or under a lowrefractive index layer of the multilayered stack.

The electrically conductive layer has to be sufficiently thin so as notto impair transparency of the antireflection coating. Generally, itsthickness ranges from 0.1 to 150 nm and better from 0.1 to 50 nm,depending on its nature. A thickness lower than 0.1 nm does generallynot allow to obtain a sufficient electrical conductivity, while athickness higher than 150 nm does generally not allow to obtain therequired transparency and low absorption characteristics.

The electrically conductive layer is preferably made from anelectrically conductive and highly transparent material. In such a case,its thickness preferably ranges from 0.1 to 30 nm, more preferably from1 to 20 nm and even more preferably from 1 to 15 nm. The electricallyconductive layer preferably comprises a metal oxide chosen from indiumoxides, tin oxides, zinc oxides and mixtures thereof. Indium-tin oxide(In₂O₃:Sn, indium oxide doped with tin) and tin oxide (In₂O₃) arepreferred. According to the most preferred embodiment of the invention,the electrically conductive and optically transparent layer is anindium-tin oxide layer, abbreviated as ITO.

Generally, the electrically conductive layer contributes to theanti-reflection properties and is a high refractive index layer of theAR coating. Examples are layers made from an electrically conductive andhighly transparent material such as ITO layers.

The electrically conductive layer may also be a very thin noble metallayer (Ag, Au, Pt, etc.), typically of less than 1 nm thick, preferablyof less than 0.5 nm thick.

As a particularly advantageous characteristic, the multilayered stack ofthe antireflection coating comprises at least four dielectric layers,preferably four or five, and optionally one electrically conductivelayer which imparts to the article its antistatic properties.

In a preferred embodiment of the invention, the antireflection coatingof the invention comprises, in the deposition order onto the substratesurface, a bilayered SiO₂ sub-layer with a thickness greater than orequal to 75 nm in accordance with the invention, a ZrO₂ layer, typicallywith a thickness of from 10 to 40 nm and preferably of from 15 to 35 nm,a SiO₂ layer or a SiO₂/Al₂O₃ layer, preferably a SiO₂/Al₂O₃ layertypically with a thickness of from 10 to 40 nm and preferably of from 15to 35 nm, a TiO₂ layer, typically with a thickness of from 40 to 150 nm,preferably of from 50 to 120 nm, a ZrO₂ layer, typically with athickness of from 8 to 30 nm and preferably of from 10 to 25 nm,optionally an electrically conductive layer, preferably an ITO layer,typically with a thickness of from 0.1 to 30 nm, preferably of from 1 to20 nm, and a SiO₂ layer or SiO₂/Al₂O₃ layer, preferably a SiO₂/Al₂O₃layer typically with a thickness of from 40 to 150 nm, preferably offrom 50 to 100 nm.

It is preferred that the multilayered stack of the invention comprisesan electrically conductive layer, and more preferred that the article ofthe invention comprises a stack composed of TiO₂/ZrO₂/electricallyconductive layer, the first layer mentioned being the nearest from thesubstrate.

According to a particularly preferred embodiment of the invention, aresuccessively deposited, starting from the surface of the substrateoptionally coated with one or more functional coatings, a SiO₂ sub-layeraccording to the invention with a thickness greater than or equal to 120nm composed of two adjacent layers formed preferably from the samematerial, a ZrO₂ layer with a thickness of from 20 to 30 nm, aSiO₂/Al₂O₃ layer with a thickness of from 20 to 30 nm, a TiO₂ layer witha thickness of from 75 to 110 nm, a ZrO₂ layer with a thickness of from10 to 20 nm, an ITO layer with a thickness of from 2 to 18 nm, and aSiO₂/Al₂O₃ layer with a thickness of from 60 to 90 nm.

The electrically conductive layer, which is typically a high refractiveindex layer of the antireflection stack, may be deposited according toany suitable method, for example by vacuum evaporation deposition,preferably ion-beam-assisted (IAD), or by means of a cathode sputteringor ion beam method.

When present, the three TiO₂/ZrO₂/electrically conductive layer(preferably ITO) successive layers are preferably all three depositedunder ion assistance (IAD), preferably under oxygen ion assistance.

The sub-layer and the multilayered stack may be deposited directly ontoa bare substrate. In some applications, it is preferred that the mainsurface of the substrate be coated with one or more functionalcoating(s) prior to depositing the antireflection coating of theinvention. These functional coatings classically used in optics may be,without limitation, an impact-resistant primer layer, an abrasion-and/or a scratch-resistant coating, a polarized coating, a photochromiccoating, an antistatic coating or a colored coating.

The sub-layer and the multilayered stack are preferably deposited ontoan abrasion- and/or scratch-resistant coating. The abrasion- and/orscratch-resistant coating may be any layer classically used as anabrasion- and/or scratch-resistant coating in the field of ophthalmiclenses.

The abrasion- and/or scratch-resistant coatings are preferablypoly(meth)acrylate- or silane-based hard coatings, comprising typicallyone or more inorganic fillers so as to improve the hardness and/or therefractive index of the coating once cured.

Abrasion- and/or scratch-resistant hard coatings are preferably preparedfrom compositions comprising at least one alkoxysilane and/or or ahydrolyzate thereof, resulting for example from a hydrolysis with ahydrochloric acid solution. After the hydrolysis step which typicallylasts for 1 to 24 h, preferably for 2 to 6 h, condensation and/or curingcatalysts may optionally be added. A surfactant is also preferably addedto the composition so as to improve the optical quality of the deposit.

Recommended coatings according to the invention include coatings basedon epoxysilane hydrolyzates such as those described in the patents FR2702486 (EP 0614957), U.S. Pat. No. 4,211,823 and U.S. Pat. No.5,015,523.

Many examples of condensation and/or curing catalysts that may besuitably used are given in “Chemistry and Technology of the EpoxyResins”, B. Ellis (Ed.) Chapman Hall, New York, 1993 and “Epoxy ResinsChemistry and Technology” 2d edition, C. A. May (Ed.), Marcel Dekker,New York, 1988.

A preferred abrasion- and/or scratch-resistant coating composition isdisclosed in the French patent FR 2702486, in the name of the applicant.It comprises an epoxy trialkoxysilane and dialkyl dialkoxysilanehydrolyzate, colloidal silica and a catalytic amount of analuminium-based curing catalyst such as aluminium acetylacetonate, theremaining of the composition being essentially comprised of solventstypically used for formulating these compositions. Preferably, thehydrolyzate used is a γ-glycidoxypropyltrimethoxysilane (GLYMO) anddimethyldiethoxysilane (DMDES) hydrolyzate.

The abrasion- and/or scratch-resistant coating composition may bedeposited onto the main surface of the substrate by dip-coating orspin-coating. It is then cured by means of the appropriate method(preferably thermal curing, UV-curing).

The thickness of the abrasion- and/or scratch-resistant coatingtypically varies from 2 to 10 μm, preferably from 3 to 5 μm.

Prior to depositing the abrasion- and/or scratch-resistant coating, itis possible to deposit onto the substrate a primer coating to improvethe impact resistance and/or the adhesion of the subsequent layers inthe end product.

Such coating may be any impact-resistant primer layer classically usedfor articles made from a transparent polymer material, such asophthalmic lenses.

Preferred primer compositions include for example thermoplasticpolyurethane-based compositions, such as those described in the Japanesepatents JP 63-141001 and JP 63-87223, poly(meth)acrylic primercompositions, such as those described in the American patent U.S. Pat.No. 5,015,523, thermosetting polyurethane-based compositions, such asthose described in the patent EP 0404111 and poly(meth)acrylic typelatex- or polyurethane type latex-based compositions, such as thosedescribed in the patents U.S. Pat. No. 5,316,791 and EP 0680492.

Polyurethane-based compositions and latex-based compositions are thepreferred primer compositions, particularly polyurethane latex typeprimer compositions.

The poly(meth)acrylic type latexes are latexes of copolymers mainlycomposed of a (meth)acrylate, such as for example ethyl, butyl,methoxyethyl or ethoxyethyl (meth)acrylate, with a generally minoramount of at least one other co-monomer, such as for example styrene.

Preferred poly(meth)acrylic latexes are latexes of acrylate and styrenecopolymers. Such latexes of acrylate and styrene copolymers arecommercially available from the ZENECA RESINS company under the tradename NEOCRYL®.

Polyurethane latexes are also known and commercially available. To bementioned as suitable examples are polyester unit-containingpolyurethane latexes. Such latexes are also marketed by the ZENECARESINS company under the trade name NEOREZ® and by the BAXENDENCHEMICALS company under the trade name WITCOBOND®.

Marketed primer compositions to be suitably used according to theinvention include the Witcobond® 232, Witcobond® 234, Witcobond® 240,Witcobond® 242, Neorez® R-962, Neorez® R-972, Neorez® R-986 and Neorez®R-9603 compositions.

Combinations of these latexes, particularly of polyurethane latexes andpoly(meth)acrylic latexes may also be used in the primer compositions.

These primer compositions may be deposited on the article sides bydip-coating or spin-coating, thereafter be dried at a temperature of atleast 70° C. and up to 100° C., preferably of about 90° C., for 2minutes to 2 hours, typically for about 15 minutes, to form primerlayers having thicknesses, after curing, ranging from 0.2 to 2.5 μm,preferably from 0.5 to 1.5 μm.

The optical article of the invention may also comprise coatings formedon the antireflection coating that may modify the surface propertiesthereof, such as hydrophobic and/or oleophobic coatings (anti-foulingtop coat). These coatings are preferably deposited onto the outer layerof the antireflection coating. The thickness thereof is generally lowerthan or equal to 10 nm, preferably ranging from 1 to 10 nm, morepreferably from 1 to 5 nm.

There are typically coatings of the fluorosilane or fluorosilazane type.They may be obtained by depositing a fluorosilane or fluorosilazaneprecursor, comprising preferably at least two hydrolyzable groups permolecule. Fluorosilane precursors preferably comprise fluoropolyethermoieties and more preferably perfluoropolyether moieties. Thesefluorosilanes are well known and are described, amongst others, in thepatents U.S. Pat. No. 5,081,192, U.S. Pat. No. 5,763,061, U.S. Pat. No.6,183,872, U.S. Pat. No. 5,739,639, U.S. Pat. No. 5,922,787, U.S. Pat.No. 6,337,235, U.S. Pat. No. 6,277,485 and EP 0933377.

A preferred hydrophobic and/or oleophobic coating composition ismarketed by the Shin-Etsu Chemical company under the trade name KP801M®. Another preferred hydrophobic and/or oleophobic coatingcomposition is marketed by the Daikin Industries company under the tradename OPTOOL DSX®. It is a fluorinated resin comprisingperfluoropropylene groups.

Typically, an optical article of the invention comprises a substratesuccessively coated with an impact-resistant primer layer, an abrasion-and/or scratch-resistant layer, a sub-layer of the invention, amultilayered antireflection stack and a hydrophobic and/or oleophobiccoating. The article of the invention is preferably an optical lens,more preferably an ophthalmic lens for eyeglasses, or an optical or anophthalmic lens blank. The lens may be a polarized lens or aphotochromic lens.

Due to its sub-layer resulting from the process according to theinvention, the optical article of the invention possesses improvedabrasion resistance properties as compared to the same article with atraditionally deposited sub-layer. These abrasion resistance propertiesmay be evaluated according to the Bayer test ASTM, described in theexperiment section.

The optical articles of the invention have preferably a BAYER valuegreater than or equal to 4.5 according to the ASTM standard F 735.81,more preferably greater than or equal to 5 and even more preferablygreater than or equal to 5.2.

The various layers of the antireflection coating have good adhesionproperties, particularly at the substrate interface. The adhesionproperties of the whole antireflection coating to the substrate havebeen controlled by means of the test ordinarily called “the n×10 blowtest”, by following the procedure described in the world patentapplication WO 99/49097.

The optical article of the invention has a high thermal resistance,evaluated through its critical temperature, defined as being thetemperature from which cracks can be observed in the antireflectioncoating. The critical temperature of an article of the invention ispreferably greater than or equal to 80° C., more preferably greater thanor equal to 85° C. and even more preferably greater than or equal to 90°C.

The optical article of the invention does not absorb or does barelyabsorb in the visible range, which means, in the context of the presentapplication, that the transmission factor thereof in the visible rangeτ_(v), also called luminous transmittance, is greater than 90%, morepreferably greater than 95%, even more preferably greater than 96% andmost preferably higher than 97%.

The τv factor does correspond to an international definition (standardISO 13666:1998) and is measured in accordance with the standard ISO8980-3. It is defined within the wavelength range ranging from 380 to780 nm.

Preferably, the light absorption of the coated article of the inventionis lower than or equal to 1%. Even preferably, the mean reflectionfactor in the visible (400-700 nm) of an article coated with anantireflection coating of the invention, written R_(m), is lower than2.5% per face, more preferably lower than 2% per face and even morepreferably lower than 1% per face of the article. In a most preferredembodiment of the invention, the article comprises a substrate both mainsurfaces of which are coated with an antireflection coating of theinvention and has a R_(m) total value (reflection values cumulatedbecause of the two faces) lower than 1%, preferably ranging from 0.7 to0.8%. The procedures to obtain such R_(m) values are well known from theman skilled in the art.

In the present application, the “mean reflection factor” is such asdefined in the standard ISO 13666:1998 and measured in accordance withthe standard ISO 8980-4, that is to say it corresponds to the averagespectral reflection from 400 to 700 nm.

The following examples are meant to illustrate the invention and are notto be interpreted as limiting the scope thereof.

EXAMPLES 1. General Procedures

The optical articles used in the examples comprise an ORMA® lenssubstrate from ESSILOR with a diameter of 65 mm, a power of −2.00diopters and a thickness of 1.2 mm, coated (except example C2) with animpact-resistant primer based on a polyurethane latex comprisingpolyester units, cured to 90° C. for 1 hour (Witcobond® 234 fromBAXENDEN CHEMICALS modified through dilution to reduce the viscositythereof, spin-coating at 1500 rpm for 10 to 15 seconds) thereafter withthe abrasion-resistant and scratch-resistant coating (hard coat)disclosed in example 3 of the patent EP 0614957 (with a refractive indexof 1.50), based on a GLYMO and DMDES hydrolyzate, colloidal silica andaluminium acetylacetonate, with an antireflection coating and lastlywith an anti-fouling coating.

Said abrasion-resistant and scratch-resistant coating was obtained bydepositing and curing a composition comprising by weight, 224 parts ofGLYMO, 80.5 parts of HCl 0.1 N, 120 parts of DMDES, 718 parts of 30% byweight colloidal silica in methanol, 15 parts of aluminiumacetylacetonate and 44 parts of ethyl cellosolve. The compositionfurther comprises 0.1% by weight relative to the total weight of thecomposition of a surfactant FLUORAD™ FC-430® from the 3M company.

The layers of the sub-layer and of the multilayered stack of theantireflection coating were deposited without heating the substrates, byvacuum evaporation, optionally, when specified, ion-beam-assisted and/orwith oxygen feeding during the deposition (evaporation source: electrongun).

The SiO₂/Al₂O₃ mixture used in the examples is L5® marketed by MerckKGaA. The antistatic layers are made from indium-tin oxide, abbreviatedas ITO, available from Optron Inc.

The anti-fouling coating was obtained by vacuum evaporation of the OF110compound provided by the Optron Inc. Company (thickness: 2-5 nm).

The device used for the deposition belongs to a Leybold 1104 apparatusfitted with an electron gun ESV14 (8 kV) for evaporating oxides, with aJoule effect crucible for depositing the top coat and with an End-Halltype ion gun (KR1 for examples 1, 2 and C1, Commonwealth Mark II forexample C2) for the preliminary phase of the substrate surfacepreparation with argon ions (IPC) and optionally for that of thesub-layer (example C1 only), as well as for depositing layers under ionassistance.

The thickness of the layers is controlled by means of a quartz scale.

2. Procedures

The process for manufacturing optical articles did comprise theintroduction of the substrate coated with a primer coating (exceptexample C2) and with an abrasion-resistant coating into a vacuumdeposition chamber, a pumping operation until a secondary vacuum wasreached, then an activation of the substrate surface using an argon ionbeam (IPC: 2 minutes, 18 cm³/min, 3 A for examples 1, 2 and C1; 2minutes, 13 sccm, 2.5 A for example C2), the interruption of the ionirradiation, the successive evaporation of the antireflection coatingrequired number of layers, a deposition of the anti-fouling coating (topcoat) and lastly a ventilation operation were performed.

Formation of the Antireflection Coating According to the Process of theInvention (Examples 1 and 2)

The process for manufacturing the antireflection coating of theinvention comprises:

-   -   The deposition of a bilayered SiO₂ sub-layer comprising: i) the        deposition onto the substrate coated of a first SiO₂ layer at a        rate of 1 nm/s (without ion assistance) until a thickness of 75        nm was reached (controlled by means of a quartz scale). The        closure element of the electron gun is closed and the        evaporation stopped; ii) the deposition onto this first layer of        a second SiO₂ layer at a rate of 1 nm/s under oxygen ion        assistance (corresponding to 15 cm³/min -2 A). The deposition of        this second layer is conducted by priming the ion gun,        preferably with the selected oxygen flow rate. Once the ion beam        has been formed and stabilized, the silica granulates are        pre-heated again with the electron gun, and the closure element        of the electron gun is opened so as to deposit 75 nm thick        silica through concomitant ion bombardment. The electron gun        closure element is closed, then the evaporation and the ion        bombardment are stopped.    -   The deposition of a multilayered antireflection stack comprising        the deposition of the first HI layer (ZrO₂) at a rate of 0.3        nm/s, the deposition of the first LI layer (SiO₂/Al₂O₃) at a        rate of 0.7 nm/s, the deposition of the second HI layer (TiO₂,        from pre-molten granulates) at a rate of 0.3-0.5 nm/s and under        oxygen ion assistance (corresponding to 15 cm³/min-2 A for        Example 1 and to 18 cm³/min-3 A for Example 2), the deposition        of a third HI layer (ZrO₂) at a rate of 0.30 nm/s and under        oxygen ion assistance (corresponding to 15 cm³/min-2 A), the        deposition of an ITO layer at a rate of 0.2-0.5 nm/s and under        oxygen ion assistance (corresponding to 15 cm³/min-2 A), and        lastly the deposition of the second LI layer (SiO₂/Al₂O₃) at a        rate of 1 nm/s.

Formation of the Antireflection Coating in the Comparative Examples C1and C2

The formation of the antireflection coating comprises the step ofdepositing the SiO₂ sub-layer onto the coated substrate at a rate of 1nm/s, under an O₂ atmosphere and a pressure of 1.5.10⁻⁴ mBar (example C1only), optionally activating the sub-layer surface by means of an argonion beam (the same treatment as IPC already performed directly on thesubstrate, example C1 only), stopping the ion irradiation, depositingthe first HI layer (ZrO₂) at a rate of 0.3 nm/s, depositing the first LIlayer (SiO₂/Al₂O₃) at a rate of 0.7 nm/s, depositing the second HI layer(TiO₂ from premolten granulates) at a rate of 0.3-0.5 nm/s, under oxygenion assistance (corresponding to 18 cm³/min-3 A for C1 and 2.5 A -120 Vfor C2), and optionally under an O₂ atmosphere (under a pressure of1.10⁻⁴ mBar, example C2 only), depositing the third HI layer (ZrO₂) at arate of 0.3 nm/s and optionally under oxygen ion assistance(corresponding to 15 cm³/min-2 A, example C1 only), depositing an ITOlayer at a rate of 0.2-0.5 nm/s and under oxygen ion assistance(corresponding to 15 cm³/min-2 A for C1 and 2.5 A -120 V for C2), andlastly depositing the second LI layer (SiO₂/Al₂O₃) at a rate of 1 nm/s.

The contents of the optical articles obtained in examples 1, 2 andcomparative examples C1 and C2 is detailed hereunder:

The sub-layer appears in grey. (a) Treatment through ion bombardment ofthe layer surface prior to depositing the next layer. (b) Oxygen supplyfor the deposition. (c) Deposition of the layer under ion assistance.

3. Characterization of the Abrasion Resistance

The abrasion resistance of the articles manufactured was evaluated bydetermining the BAYER values by means of the Bayer test (Bayer sandmethod) in accordance with the standard ASTM F 735.81, with a higherBayer value meaning a higher abrasion resistance. The Bayer sand valueis considered to be good when R is between 3.4 and 4.5, and to beoutstanding when R is equal to or higher than 4.5.

Such test consists in making simultaneously oscillate a sample glass anda reference glass with a given reciprocating motion in a tray containingan abrasive powder (about 500 g sand) with a defined particle size at afrequency of 100 cycles/minute for 2 minutes. Measurements of the sampleglass “before/after” are compared with those of a reference glass,indeed a CR-39®-based bare glass for which the BAYER value is set to 1.The Bayer sand value is R═H reference glass/H sample glass.

The diffusion measurements were conducted using a Hazeguard system modelXL-211 manufactured by Pacific Scientific.

4. Results

The results of the abrasion resistance measurements are given in Table 1hereunder.

TABLE 1 Bayer Test ASTM (BAYER Example SAND) 1 6.0 2 5.4 Comparative 14.7 Comparative 2 4.8

The lenses of examples 1 and 2 have a better abrasion resistance thanthose of the comparative examples do.

1.-23. (canceled)
 24. An optical article with antireflection properties,comprising a substrate having at least one main surface coated with anantireflection coating comprising, starting from the substrate: asub-layer comprising two adjacent layers, the sum of the thicknesses ofthe two adjacent layers being greater than or equal to 75 nm; and amultilayered antireflection stack comprising at least one highrefractive index layer and at least one low refractive index layer,wherein the deposition of the first of the sub-layer two adjacent layershas been carried out without ion assistance and the deposition of thesecond of the sub-layer two adjacent layers has been carried out underion assistance.
 25. The article of claim 24, wherein the two adjacentlayers of the sub-layer are formed from the same material.
 26. Thearticle of claim 24, wherein the thickness ratio of the sub-layer twoadjacent layers to each other varies from 9:1 to 1:9.
 27. The article ofclaim 26, wherein the thickness ratio of the sub-layer two adjacentlayers to each other varies from 4:6 to 6:4.
 28. The article of claim24, wherein the sum of the thicknesses of the two adjacent layers isgreater than or equal to 80 nm.
 29. The article of claim 28, wherein thesum of the thicknesses of the two adjacent layers is greater than orequal to 100 nm.
 30. The article of claim 29, wherein the sum of thethicknesses of the two adjacent layers is greater than or equal to 150nm.
 31. The article of claim 24, wherein the sub-layer two adjacentlayers are SiO₂-based layers.
 32. The article of claim 31, wherein thesub-layer two adjacent layers are free of Al₂O₃.
 33. The article ofclaim 31, wherein the sub-layer two adjacent layers consist of SiO₂layers.
 34. The article of claim 24, wherein the sub-layer comprises, inaddition to the two adjacent layers, at most three layers interleavedbetween the substrate and the two adjacent layers.
 35. The article ofclaim 24, further defined as comprising an ASTM BAYER value greater thanor equal to 4.5 of the standard ASTM F 735.81.
 36. The article of claim24, wherein all the low refractive index layers of the multilayeredstacks comprise a mixture of SiO₂ and Al₂O₃.
 37. The article of claim36, wherein all the low refractive index layers of the multilayeredstacks consist of a mixture of SiO₂ and Al₂O₃.
 38. The article of claim24, wherein the high refractive index layers of the multilayered stackcomprise at least one of TiO₂, PrTiO₃, or ZrO₂, or combinations thereof.39. The article of claim 24, further defined as an ophthalmic lens. 40.A process for manufacturing an optical article with antireflectionproperties, comprising: providing an optical article comprising asubstrate having at least one main surface; depositing onto a mainsurface of the substrate a sub-layer having an exposed surface, wherethe sub-layer comprises two adjacent layers, the sum of the thicknessesof the two adjacent layers being greater than or equal to 75 nm;depositing onto the exposed surface of the sub-layer a multilayeredantireflection stack comprising at least one high refractive index layerand at least one low refractive index layer, recovering an opticalarticle comprising a substrate having one main surface coated with anantireflection coating comprising the sub-layer and the multilayeredstack, wherein the deposition of the first of the sub-layer two adjacentlayers is carried out without ion assistance and the deposition of thesecond of the sub-layer two adjacent layers is carried out under ionassistance.
 41. The process of claim 40, wherein the two adjacent layersof the sub-layer are formed from the same material.
 42. The process ofclaim 40, wherein the sum of the thicknesses of the two adjacent layersis greater than or equal to 80 nm.
 43. The process of claim 42, whereinthe sum of the thicknesses of the two adjacent layers is greater than orequal to 100 nm.
 44. The process of claim 43, wherein the sum of thethicknesses of the two adjacent layers is greater than or equal to 150nm.
 45. The process of claim 40, wherein the sub-layer two adjacentlayers are SiO₂-based layers.
 46. The process of claim 45, wherein thesub-layer two adjacent layers are free of Al₂O₃.
 47. The process ofclaim 45, wherein the sub-layer two adjacent layers consist of SiO₂layers.
 48. The process of claim 40, wherein the deposition of each ofthe sub-layer of the antireflection coating layers is carried out byvacuum evaporation.
 49. The process of claim 40, wherein, prior todepositing the sub-layer, the surface of the substrate is submitted to aphysical or a chemical activation treatment selected from a bombardmentusing energetic species, a corona discharge treatment, an ion spallationtreatment, an ultraviolet treatment or a plasma treatment under vacuum,an acid or base treatment and/or a solvent treatment, or combinations ofthese treatments.
 50. The process of claim 40, wherein the deposition ofone or more of the multilayered antireflection stack layers is carriedout under ion assistance.
 51. The process of claim 40, wherein thethickness ratio of the sub-layer two adjacent layers to each othervaries from 9:1 to 1:9.
 52. The process of claim 51, wherein thethickness ratio of the sub-layer two adjacent layers to each othervaries from 4:6 to 6:4.